1. Field of the Invention
The present invention relates to a screw, a mixer and an extruder which have a heat exchange function, and more particularly relates to a screw, a mixer and an extruder which have a heat exchange function enabling to supply a heat exchange medium without fatigue fracture of a heat exchange medium supply pipe even if the screw is bent and deformed during mixing and extrusion.
2. Description of the Related Art
In a mixer or an extruder which mixes or extrudes a raw material including thermoplastic resin such as resin and a rubber material, it is important for the quality of a product to adjust the temperature of the raw material being mixed or extruded, and to prevent the raw material from being over heated, attaching to a screw, and deteriorating. Hence, a medium communication hole (referred to as a heat exchange medium chamber hereinafter) is provided in the screw of the mixer and the extruder, and the screw is constituted such that the temperature is controlled by supplying a heat exchange medium such as liquid coolant into the heat exchange medium chamber.
In more detail, in the screw, there is formed the heat exchange medium chamber which is located at a center section in the radial direction, runs along the lengthwise direction, and has an opening on one shaft end. A heat exchange medium supply pipe is fit into the liquid coolant chamber through a rotary joint. In this case, the heat exchange medium supplied through the rotary joint flows through the heat exchange medium supply pipe, and flows out from an extreme end of the heat exchange medium supply pipe. The liquid coolant flowing out from the extreme end of the heat exchange medium supply pipe collides with a terminal end of the heat exchange medium chamber, and changes its direction toward a base end direction of the heat exchange medium supply pipe. The heat exchange medium then flows in a flow passage in a cylindrical shape formed between an outer periphery of the heat exchange medium supply pipe and an inner wall of the heat exchange medium chamber, and then flows out through the rotary joint.
There are two types of the heat exchange medium supply pipe which supplies the heat exchange medium into the heat exchange medium chamber of the screw of the mixer or the extruder. One type is constituted by one pipe, and the other type is constituted by connecting multiple pipes. Supports whose extreme end is in contact with the inner wall of the heat exchange medium chamber are provided at multiple locations in the lengthwise direction on the outer periphery of the heat exchange medium supply pipe of the former type. Namely, it is intended that the supports cause the center of the heat exchange medium supply pipe to coincide with the center in the radial direction of the heat exchange medium chamber. As for the heat exchange medium supply pipe of the latter type, multiple pipes are connected by threadedly attaching the pipes to pipe joints also serving as a support. The pipe joints also serving as the support cause the center of the heat exchange medium supply pipe to coincide with the center in the radial direction of the heat exchange medium chamber (for example, see Japanese Patent Publication No. 2778797).
Since the screw of the mixer or the extruder receives an offset load (bending force) from the raw material during the operation of the mixer or the extruder, the screw rotates while yielding. As a result, the highly rigid heat exchange medium supply pipe made of metal and the like is forcefully displaced repeatedly by the yield of the screw, and consequently, the heat exchange medium supply pipe may be fatigue-fractured. If the heat exchange medium supply pipe is fatigue-fractured, since cooling function (heat exchange function) provided for the screw decreases, it is impossible to adjust the temperature of the raw material being mixed or extruded, or to prevent the raw material which has melted, has being over heated, and has attached to the screw from deteriorating.
As a result, since it is necessary to stop the operation of the mixer or the extruder for maintenance, there has been such a problem to be solved that it is not possible to expect an increase of the productivity of a mixed material or extruded products due to the decrease of the availability of the mixer or the extruder in addition to a disadvantage in terms of the running cost of the mixer or the extruder.